U.S. Pat. No. 5,380,965 (belonging to the same applicant) discloses an electromechanical pulse generator having a purely mechanical mode of operation for microelectronic equipment, e.g. volume control in hearing aids, consisting of a housing formed by a fixed base portion in which a shaft is fixedly mounted. A timing wheel is rotatably mounted around the shaft, the timing wheel having the form of a downward facing open cylinder and being fixedly connected to a casing which forms an external handle. The inner cylinder surface of the timing wheel is provided with grooves engaging with a protrusion of a circular carrier rotatably mounted around the shaft.
A U-shaped contact spring has members which are individually imparted an oscillating movement between contact pairs A-B-C and A-D-E, respectively, by the turn of the timing wheel in one or the other direction via the carrier which can only move over a pre-determined circular section, so as to generate digital pulse trains. A locking device prevents the carrier from moving beyond the pre-determined circular section and causes the protrusion to continuously engage with the grooves by the turn of the timing wheel.